The invention relates to a magnetoresistive magnetic field sensor comprising a bilayer with a first soft magnetic layer and in direct contact therewith a second soft magnetic layer, said layers being exchange coupled to one another, the electrical resistivity of the first soft magnetic layer being higher than that of the second soft magnetic layer.
In such a magnetoresistive magnetic field sensor it is of advantage to obtain a magnetoresistance ratio (MR-value) which, also with a relatively small external magnetic field, is sufficient to perform an accurate measurement of the change in the resistivity due to a rotation of the magnetization vector in the bilayer by the external magnetic field. This magnetoresistance ratio is deducted from the resistance value of the sensor in both the absence (R.sub.o) and the presence (R.sub.s) of an external magnetic field: ##EQU1##
From Kamiguchi et al; Giant magnetoresistance and soft magnetic properties of Co.sub.90 Fe.sub.10 /Cu spin-valve structures, J. Appl. Phys. 79 (8), Apr. 15, 1996, it is known to deposite a NiFe/CoFe layer on a soft magnetic layer, e.g. a CoNbZr layer. In such a bilayer structure with a NiFe/CoFe layer deposited on a CoNbZr layer, the NiFe/CoFe layer has a relatively low electrical resistivity, while the CoNbZr layer has an electrical resistivity which is about a factor of 4 larger than that of the NiFe/CoFe layer. Although the NiFe/CoFe material demonstrates a relatively large anisotropic magnetoresistance effect, the relatively low electrical resistivity of these materials forms a limiting factor in the measurement thereof.